1. Field of the Invention
The present invention relates to an apparatus for measuring weights of articles which have various configurations and are successively transported into a measuring area, and also relates to an apparatus for measuring weights and lengths of articles having various configurations and being successively transported into measuring area.
2. Related Art Statement
It is rather difficult to measure weights and lengths of articles having various shapes, which are successively transported on a belt conveyer into a measuring area in such a manner that distances between successive articles are very small, without stopping the belt conveyer.
Heretofore, a weighing conveyer having a high response is generally used to measure weights of articles successively fed along a belt conveyer. Since such a weighing conveyer has been well known in the high speed automatic weighing technique, its detailed explanation is dispensed with.
Now a known weight measuring apparatus using a weighing conveyer having a single weighing range will be explained with reference to numerical examples.
FIG. 1 is a schematic view showing a known weighing apparatus for measuring weights of relatively long articles. An article A whose weight is to be measured is transported from an input side conveyer 1 into a weighing conveyer 2 having a length D=80 cm, and after measurement the article A is transported onto an output side conveyer 3. At a front edge of the weighing conveyer 2 is arranged a photo-sensor 4 in the form of a photo-interrupter. When the article is transported from the input side conveyer 1 onto the weighing conveyer 2 and a rear end of the article A passes through the photo-sensor 4, the photo-sensor generates an edge detection signal. For a time interval during which the article A is transported over a predetermined minimum distance S such as 10 cm after the generation of the edge detection signal, the weighing conveyer 2 performs the weighing operation. Said minimum distance S is required for measuring a weight of an article. In this manner, a weight of the article A can be measured correctly. However, if a length L of the article A is larger than 70 cm, the weighing conveyer 2 measures a weight of the article in such a condition that a front portion of the article A is placed on the output side conveyer 3. It is apparent that a weight of the article A could not be measured correctly under such a condition.
FIG. 2 is a schematic view of another known weighing apparatus which is usually used in measurement of relatively short articles. A basic conception of this known weighing apparatus is substantially identical with that of the apparatus shown in FIG. 1. In this apparatus, in order to measure a weight of an article A, a preceding article A' should be completely placed removed from the weighing conveyer 2. To this end, a second photo-sensor 5 is arranged at a rear end of the weighing conveyer 2. Then, a measured value obtained by the weighing conveyer 2 after the second photo-sensor 5 has detected the rear edge of the preceding article A' is adopted as a final measured value. Therefore, when a space G between successive articles A', A and A" is 35 cm and a length L of articles is smaller than 20 cm, two articles might be simultaneously placed on the weighing conveyer 2. Similarly, when a space G is 25 cm and a length L of articles is smaller than 40 cm, two successive articles might be placed on the weighing conveyer 2. In such cases, weights of articles could never be measured correctly.
Now a maximum length L.sub.max of the article A which can be measured correctly by the weighing conveyer 4 in the apparatuses shown in FIGS. 1 and 2 will be considered. In FIG. 1, in order to measure a weight of the article A under such a condition that the preceding article A' or succeeding article A" is not placed on the weighing conveyer 2 together with the article A so that the correct measurement can be carried out, that is to say, a space G between successive articles is not less than the minimum travelling distance S which is necessary for measuring a weight of articles accurately, the measurement has to be carried out during a time interval in which a front end of the article A travels over a portion 10 cm of the weighing conveyer 2, said portion being indicated by a thick arrow S. Then, as can be understood from FIG. 1, the maximum length L.sub.max of the article A can be given by the following equation (1): EQU L.sub.max =D-S (1)
In this case, a space G between successive articles may be set to an arbitrary value which satisfies the condition G.gtoreq.S. Therefore, the maximum length L.sub.max of the article A is determined by the effective length D of the weighing conveyer 2 and the effective minimum distance S. In this manner, in the apparatus shown in FIG. 1, the maximum length L.sub.max of the article A can be calculated as follows: EQU L.sub.max =80 cm-10 cm=70 cm
Now a minimum length L.sub.min of the article A will be determined. As illustrated in FIG. 2, the minimum length L.sub.min of the article A is greatly dependent upon the space G between successive articles and can be expressed by the following equation (2): EQU L.sub.min =D+S-2G (2)
For instance, when the space G between successive articles is 35 cm, the length D of the weighing conveyer 2 is 80 cm and the minimum distance S is 10 cm, the minimum length L.sub.min of the article A becomes 20 cm.
As stated above, the minimum length L.sub.min of the article A is affected by the space G between successive articles, and when the space G is large, a smaller article can be measured. However, in such a case, the number of articles which can be measured within a unit time becomes smaller and a measuring efficiency is decreased. It should be noted that if a space between the relevant article A and preceding articles A' differs from a space between the relevant article A and the succeeding article A", a smaller distance G is adopted in the equation (2).
By applying actual values of the article length L, minimum distance S and space G in the above equations (1) and (2), a measurable range with respect to the article length L and space G can be obtained diagrammatically. FIG. 3 is a diagram showing such a measurable range when the length D of the weighing conveyer 2 is set to 80 cm and the minimum travelling distance S is to 10 cm. It should be noted that the space G is set to be not less than 10 cm. In FIG. 3, a hatched area denotes the measurable range.
For instance, when the space G between successively transported articles on the conveyer is set to 25 cm, lengths of articles whose weights can be measured correctly is limited to a range from 40 cm to 70 cm as can be seen from a line a in FIG. 3. That is to say, an article having a length more than 70 cm or smaller than 40 cm could not be measured correctly. When articles have a predetermined length L of 25 cm, then a space G has to be set to a value not less than 32.5 cm as indicated by a line b in FIG. 3.
Actual values of the above mentioned parameters may be varied to some extent. Particularly, when parameters such as the length D of the weighing conveyer 2, minimum distance S, space G between successive articles and length L of articles are changed, the basic property of the weighing apparatus is not changed at all.
Width and height of a rectangular freight such as a cardboard box can be measured relatively easily by means of an optical measuring apparatus irrespective of a fact that the article is stopped or moved. However, a length of a moving article, i.e. a dimension of the article in a direction of the movement could not be easily measured.
In general, an ability of a high speed weighing apparatus or high speed article selecting apparatus is expressed by the number of articles which could be handled within a unit time. Therefore, also in the present specification, the number of handled articles within a unit time is adopted as a standard for judging the operation ability of the weighing apparatus.
The performance of the weighing apparatus can be improved by increasing the travelling speed or decreasing a pitch of articles (center distance or length L of article+space G). Since the present invention does not relates to the technique for performing the weight measurement at a high speed transportation, a relation between the performance of the weighing apparatus and the geometric condition of the article length L and space G will be considered.
By using the numerical examples explained above with reference to the known weighing apparatuses shown in FIGS. 1 and 2, the performance will be obtained in the following table when the transporting speed is set to 100 cm/sec. In this table, an inverse of the performance corresponds to the pitch P (cm), and the pitch P is a sum of the article length L and space G between successive articles. Even when the article length L is decreased to a half thereof , the performance is not increased twice, but an increment of the performance is at most 30%.
TABLE ______________________________________ L G P performance ______________________________________ 10 40 50 2.00 20 35 55 1.82 30 30 60 1.67 40 26 65 1.54 50 20 70 1.43 60 15 76 1.33 70 10 80 1.25 ______________________________________ L article length (cm) G minimum space (cm) p minimum pitch (cm)
As can be seen from the above table, in the known weighting apparatuses using a single weighing conveyer 2, when the space G between successively transported articles is set to a small value for attaining a higher performance, the length L of articles which can be measured correctly is limited to a relatively large value. That is to say, in such a condition, two articles having a small length might be placed on the weighing conveyer 2 simultaneously and thus could not be measured correctly. On the other hand, when the space G is set to a relatively large value in order to measure articles having smaller length L, the performance of the weighing apparatus is decreased.
Moreover, it is technically very difficult to measure a length of an article as well as its weight while the article is continuously transported on the conveyer.